The present invention relates to an apparatus and method for controlling a fluid control valve and more particularly to an apparatus and method for periodically actuating a hydraulic control valve of an compression release brake system of an internal combustion engine and reduce silting in the hydraulic control valve.
Compression release engine brakes or engine retarders are used to assist and supplement wheel brakes in slowing heavy machines such as earthmoving vehicles, off and on highway trucks, buses and the like. Compression release engine brakes often utilize an actuator that is fluid operated to mechanically move an engine valve at an appropriate timing to achieve compression release braking. Opening an exhaust valve on a compression stroke of the engine at or near top dead center of an engine piston causes the engine cylinder to blow down and exhaust the compressed air in the cylinder to atmosphere. At an appropriate time during the intake stroke of the engine the engine valve is closed. This cycle is repeated over and over again with respect to the each engine cylinder until braking is no longer needed. This allows the engine to develop a retarding horsepower which may be a substantial portion of the operating horsepower developed by the engine in its operating mode.
In some compression release brake systems, an opening and closing of the exhaust valve at the end of the compression stroke may be performed by a hydraulically operated actuator having a piston and a plunger. A control valve having a spool may be provided to controllably connect the hydraulically operated actuator to a source of high pressure fluid, such as a hydraulic rail of a hydraulically actuated fuel system. Each time a compression release event is desired for an engine cylinder, the hydraulic control valve is actuated in order to deliver high pressure hydraulic oil to the actuator which mechanically opens the exhaust valve.
Under normal operating conditions, the control valve is actuated very infrequently, e.g., the control valve may be actuated less than 5% of the engine operating time. Therefore, due to debris in the hydraulic fluid and the presence of the relatively high pressure of the hydraulic fluid, e.g., on the order of 5-31 MPa, at an inlet port of the hydraulic control valve, silting may occur in a sealing clearance between the spool and the body of the control valve at a location adjacent the inlet port of the hydraulic control valve. That is, impurities, such as metallic and non-metallic particles contained in the fluid may be deposited and compacted over time at the inlet port of the control valve. As a result, silting in the control valve may cause the control valve to function improperly by delaying or possibly precluding valve opening.
The occurrence of silting is dependent upon several factors such as valve sealing clearances, debris particle size, the pressure of the hydraulic fluid and the level of debris in the hydraulic fluid. The level of impurities in the fluid may be based upon the source and application of the hydraulic fluid and may increase over time due to the operating environment of the engine. Further, the pressure of the hydraulic fluid generally required to produce silting is on the order of about 7 MPa.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention, a control system has an actuator, a source of high pressure fluid flow, and a fluid reservoir. The actuator has a plunger movable between an extended position and a retracted position. A control valve having a spool movable between a first position and a second position is connected to the actuator, the source of high pressure fluid flow, and the reservoir. The control valve is adapted to deliver fluid flow from the actuator to the reservoir at the first position of said spool and is adapted to deliver high pressure fluid flow from the source to the actuator at the second position of the spool. An electronic control module is connected in control communication with the control valve and is adapted to deliver a control signal to the control valve. The control valve spool is movable to a one of said first and second positions in response to receiving the control signal. The electronic control module automatically delivers the control signal to the control valve in response to a predetermined elapsed time during which the control valve is at the one of the first and second positions being greater than a predetermined time.
In another aspect of the present invention a compression release engine brake system has an engine cylinder, a source of high pressure fluid flow, a fluid reservoir, and an exhaust valve disposed in the engine cylinder and movable between a first position at which fluid flow is blocked from leaving the cylinder and a second position at which fluid flow is passable from the cylinder and an actuator having a plunger movable between extended position and a retracted position. The plunger is connected to move the exhaust valve between the first and second positions respectively in response to movement of the actuator between the retracted and extended positions. A control valve has a spool movable between a first position and a second position. The control valve is connected to the actuator, the source of high pressure fluid flow, and the reservoir. The control valve is adapted to deliver fluid flow from the actuator to the reservoir at the first position of said spool and is adapted to deliver high pressure fluid flow from the source to the actuator at the second position of the spool and move said actuator from the retracted position to the extended position. An electronic control module is connected in control communication with the control valve and adapted to deliver a control signal to the control valve. The control valve spool is movable to the second position in response to receiving the control signal. The electronic control module automatically delivers the control signal to the control valve in response to a predetermined elapsed time during which the control valve is at the first position being greater than a predetermined time.
In another aspect of the present invention, a method of controlling a control valve associated with an internal combustion engine is provided. The control valve has a spool movable between a first position and a second position, a second port and a third port. The method includes the steps of monitoring an amount of elapsed time since the control valve spool was last moved; moving the control valve spool to the second position; and coupling the second port to the third port when the amount of elapsed time exceeds a predetermined time in order to discharge debris accumulated at the second port.
In yet another aspect of the present invention, a work machine, has an engine, an exhaust valve attached to the engine and operative to move between an open position and a closed position, a fluid operated actuator operatively connected to said exhaust valve and adapted to move the exhaust valve to the open position, a reservoir, a source of high pressure fluid source adapted to supply a high pressure action fluid and a control valve connected to the hydraulic control valve and movable between a first position operable to connect the actuator to a low pressure fluid source and a second position operable to connect the actuator to the source of high pressure fluid. An electronic control module connected in control communication with the control valve is adapted to generate a control signal to position the control valve in the second position when an elapsed time, during which the control valve is in the first position, is greater than a predetermined time.